Nitrous oxide (N2O) is a long-lived stratospheric ozone-depleting substance and greenhouse gas with a current atmospheric lifetime of 116±9 yr. The concentration of atmospheric N2O has increased by over 20% from 270 parts per billion (ppb) in 1750 to 331 ppb in 2018, with the fastest growth observed in the past five decades. In the coming decades, N2O emissions are expected to continue increasing due to the growing demand for food, feed, fiber and energy, as well as from waste generation and industrial processes. By harnessing extensive data from multiple sources, both bottom-up (BU) and top-down (TD) methods and their cross-constraints, here we present a comprehensive, consistent analysis and synthesis of the global N2O budget across all sectors, including natural and anthropogenic sources and sinks. BU approaches include emission inventories, spatial extrapolation of field flux measurements, nutrient budget modeling, and process-based modeling for land and ocean fluxes. The TD approaches combine measurements of N2O mole fractions with atmospheric transport models in statistical optimization frameworks (inversions) to constrain the underlying sources and sinks. We constructed a total of 43 flux estimates including 30 with BU approaches, five flux estimates with TD approaches, and eight other estimates with observation and modeling approaches.
Results/Conclusions
With this extensive data and BU/TD framework, we establish the most comprehensive global and regional N2O budgets that include 18 sources and different versions of its chemical sink. With the construction of these budgets, we explore the relative temporal and spatial importance of multiple sources and sinks driving the atmospheric burden of N2O, their uncertainties, and interactions between anthropogenic forcing and natural fluxes of N2O as an emerging climate feedback. Each of the past four decades had higher global N2O emissions than the previous one, and in all, agricultural activities dominated the growth. we also find that China, India and Brazil dominate the regional contributions to the excess N2O in the most recent decade. Our extensive database and modelling capability also fill out current gaps in national and regional emissions inventories. Reducing excess use of N applications to croplands and adopting precision fertilizer application methods provide the largest immediate opportunities for N2O emissions abatement. Our assessment enhances understanding of the global N cycle and will inform policy development for N2O mitigation, ideally helping to curb warming to levels consistent with the long-term goal of the Paris Agreement.